The present invention relates to a positioning device for bucket loaders and more particularly to an improved system utilizing an electrical switch and actuating means mounted upon the telescoping cylinder and rod members of the tilt jack to terminate operation of the tilt jack as the bucket is moved to a preferred position on the loader.
Typically, bucket loaders have a bucket pivotably supported by lift arms with hydraulically operated tilt jacks interconnected between the lift arms and the bucket by suitable tilt linkage, the operation of the tilt jacks being controlled by a manually operable hydraulic valve having two operating positions. Movement by the operator of the valve to one of its operating positions will cause the tilt jacks to pivot the bucket upwardly to a rack-back position, while movement of the valve to its other operating position will cause the tilt jacks to pivot the bucket in the opposite direction, downwardly to dump position. Movement of the valve from its operating position to a non-operating position will stop tilting movement of the bucket by the tilt jacks and will hold the bucket at the position to which it has been moved by the tilt jacks. When the bucket is other than in its load position, i.e., the position wherein the floor of the bucket is parallel to the ground, the bucket may be moved and positioned at load position by moving the control valve to the appropriate operating position so that the tilt jacks will pivot the bucket towards the load position and by releasing the valve when the bucket has reached load position.
Positioning of the bucket in load position can be done by manipulation of the control valve by the operator. However, it is much more desirable to provide a means for automatically positioning the bucket at the intermediate load position, since such position is relatively critical and the operator's view of the bucket is generally obstructed as the bucket is approaching ground level. Since the position of the bucket at any moment is a function of the degree of extension or retraction of the tilt jack, it is common to use such extension to actuate an automatic positioning control.
Bucket loaders of the type contemplated herein normally employ detented tilt control valves to hold the control handle for the valve in rack-back or dump position when moved thereto so that the operator can release the control handle after the valve has been moved to its desired operating condition and the valve will stay in that position. Sufficient force by the operator on the control handle will enable him to pull the valve from its detent held position. It is desirable to provide means for rendering the detent mechanism inoperative as the handle is moved rapidly back and forth between rack-back and dump positions during a fishtailing loading operation to facilitate operator control over the bucket during loading.
Various types of position-control systems for bucket loaders have been proposed. Typically, such controls are hydraulically, mechanically, electrically or electronically controlled.
Hydraulic positioning systems suffer from control problems when malfunctions occur in the hydraulic system. For example, a leak in the slave cylinder or in the hydraulic circuits can cause bucket drifting ranging from slight movement to drifting simulating a slow dump. A broken supply line almost completely incapacitates the positioning control system. External repairs are time-consuming, particularly if the line to the tank has to be replaced. If an internal repair or adjustment has to be made in the hydraulic system, it is generally necessary to drain the hydraulic tank, which causes excessive down-time.
Electrical positioning systems overcome most of the above problems inherent in hydraulic systems, in that they are more reliable, more readily serviced, and are external and thus independent of the main hydraulic apparatus. However, most electrical positioning systems utilize microswitch means mechanically coupled to cams, recessed rods, etc., attached to the positioning hydraulic cylinder to indicate the position of the bucket. See, for instance, U.S. Pat. No. 3,420,393. Thus, such a combination is subject to wear, dirt, vibration, etc., common to earthmoving apparatus, with the associated maintenance and breakdown problems.
An improved approach is disclosed in U.S. Pat. No. 3,519,155, wherein a proximity switch is mounted on the tilt jack cylinder to be actuated by a magnet mounted on the tilt jack rod, the switch controlling directly a solenoid in the detent disabling mechanism. This approach reduces considerably the fouling of the system by dirt and debris. By use of a sufficiently long magnet this approach also allowed the detent mechanism to be inoperative during loading operations. However, this approach requires the proximity switch to handle the full solenoid current and requires the use of a relatively expensive, long magnet to maintain the switch closed during loading operations.
A further approach is that disclosed in U.S. Pat. No. 3,782,248 wherein two proximity switches are mounted on the tilt jack cylinder and a single small magnet is mounted on the tilt jack rod. Sequential and momentary actuation of the switches by movement of the magnet past the switches in the proper direction causes signals to be fed to an electronic logic circuit which then it turn causes the bucket to be positioned in load position while allowing "detent" action to be inoperative during a loading operation. Although this approach does not require the proximity switches to handle large currents and eliminates the substantial cost of a long magnet, the cost of the electronic logic circuit is relatively high.